NO₃^– Promotes Nitrogen-Containing Disinfection Byproduct Formation in Corroded Iron Drinking Water Pipes

Nitrogen-containing disinfection byproducts (N-DBPs) are highly toxic DBPs in drinking water. Though, under normal conditions, NO3– could not directly participate in disinfection reactions to generate N-DBPs, here, we first found that NO3– could promote the formation of N-DBPs in corroded iron drinking water pipes. The coexistence of corrosion produced Fe(II) and iron oxides is a critical condition for the transformation of N species; meanwhile, most of the newly generated N-DBPs had aromatic fractions. The Fe–O–C bond formed between iron corrosion products and natural organic matter promoted electron transfer for the N transformation with pyrrolic N as the intermediate N species. Density functional calculation confirmed that the coexistence of Fe(II) and iron oxides effectively reduced the Gibbs free energy for NO3– reduction. ΔG of the key rate-determining step from NO* to NOH* decreased from 1.55 eV on FeOOH to 1.35 eV on Fe(II)+FeOOH. In addition, the large decrease of cell viability of the water samples from 74.3% to 45.4% further confirmed the formation of highly toxic N-DBPs. Thus, in a drinking water distribution system with corroded iron pipes, the low toxic NO3– may increase toxicity risks via N-DBP formation

Anchor weights and sizes.

<p>Anchor weights and sizes.</p

Schematic diagram of falling movement of the anchor for ordinary anchoring.

<p><i>h</i>_<i>1</i>- height of the anchor-dropping position above the water surface, m; <i>h</i>_<i>2</i>- height of water surface above the bottom of the water, m; <i>h</i>_<i>3</i>- depth that the anchor penetrates into the seabed, m.</p

Schematic diagram of falling movement of the anchor during a deep water anchoring operation.

<p>Schematic diagram of falling movement of the anchor during a deep water anchoring operation.</p

Parameters of the ship’s Hall anchor.

<p>Parameters of the ship’s Hall anchor.</p

Required burial depth for submarine pipelines so that they are protected from deep water anchoring.

<p>Required burial depth for submarine pipelines so that they are protected from deep water anchoring.</p

Variation in influences on effective burial depth of submarine pipelines for ordinary anchoring and deep water anchoring.

<p>Variation in influences on effective burial depth of submarine pipelines for ordinary anchoring and deep water anchoring.</p

Component names and size of an A type hall anchor.

<p>h- length of fluke; H- length of the anchor arm; B1- width of the anchor arm; H1- length of anchor shackle; L- length of the anchor bottom; and B- width of the anchor bottom.</p

Required burial depth for submarine pipelines for protection from ordinary anchoring.

<p>Required burial depth for submarine pipelines for protection from ordinary anchoring.</p

PFOA Increases Microbial Risk by Promoting Iron Release and Weakening Biofilm Adhesion in Unlined Iron Drinking Water Pipes

Perfluorooctanoic acid (PFOA) entering drinking water distribution system (DWDS) could induce complex processes affecting the water quality at consumer taps. Here, we first found that PFOA could greatly increase microbial risk by triggering high iron release or reducing the biofilm adhesive ability depending on the concentration levels of PFOA in unlined iron pipes. The heterotrophic plate counts (HPC) of three scenarios TP (without PFOA, control), TP100 (PFOA 100 ng/L, moderate concentration), and TP1000 (PFOA 1000 ng/L, high concentration) were 180, 692, and 192 CFU/mL, and the corresponding total iron concentrations were 0.67, 1.84, and 0.26 mg/L, respectively. Obviously, PFOA enhanced iron release in TP100 but inhibited iron release in TP1000, and the highest HPC in TP100 was in accordance with its highest iron release. Notably, TP1000 had the lowest iron release, but its HPC was the second highest. The extracellular polymeric substance (EPS) composition analysis revealed that PFOA stimulated EPS production but decreased the ratios of polysaccharides/proteins and carbohydrates/proteins, indicating that the biofilm adhesion ability was reduced due to PFOA, which was accountable for the relatively higher HPC in TP1000. This study provided new insights into the water quality risks associated with PFOA in DWDS